Heat exchangers

ABSTRACT

In a tube-in-shell heat exchanger, each tube plate is secured along its outer edge to the shell of the heat exchanger by an intermediate annular member extending across a gap between the outer edge of the tube plate and the shell, the radial crosssection of the annular member being of arched form. Thermal insulation for the tube plates consisting of a series of plate members edge on to the tube plate and arranged parallel one to another between successive rows of the heat exchanger tubes, is also described.

United States Patent mi Linning [54] HEAT EXCHANGERS [75] Inventor:David Lees Linning, Warrington,

England [73] Assignee: United Kingdom Atomic Energy Authority, London,England [22] Filed; Mays, 1972 [211 Appi.N0.;2s1,23s

[30] Foreign Application Priority Data June 25,1971 Great Britain21315811/71 May 26, 1971 Great Britain t. 17295/71 [52] U.S. Cl 165/83,165/134, 165/158 [5l] Int. Cl. F28g 7/00 [58] Field of Search 165/158,9, 83, 18167-69,

165/178; 122/32 L, 32 T, 32 S, 32 F f [56] References Cited UNITEDSTATES PATENTS 2,736,400 2/1956 Gay etal. 165/81 3,132,691 5/1964Esleeck 165/158 X 3,134,432 5/1964 Means 165/178 X PrimaryExaminer-Charles J. Myhre Assistant Examner-Theophil W. Streule, Jr.

' Attorney, Agent, or Firm-Larson Taylor & Hinds [5 7] ABSTRACT ln atube-in-shell heat exchanger, each tube plate is secured along its outeredge to the shell of the heat exchanger by an intermediate annularmember extending across a gap between the outer edge of the tubeplate-and the shell, the radial cross-section of the annular memberbeing of arched form. Thermal insulation forthetube plates consisting ofa series of plate members edge on to the tube plate and arrangedparallelone to another between successive rows of the heat exchangertubes, is also described.

9 Claims, 4 Drawing Figures HEAT EXCHANGERS BACKGROUND OF THE INVENTIONThis invention relates to heat exchangers and in particular to that kindof heat exchanger in which a bundle of parallel heat exchanger tubesextend between tube plates at either end of the bundle. The heatexchanger tubes are connected at their ends with holes in the tubeplates, for example by welding. The bundle of heat exchanger tubes isdisposed within an outer shell or container to which the tube plates aresecured.

ln one use of such a heat exchanger, for example, as a steam generatoror steam superheater, a liquid metal heat transfer medium, such assodium, is passed through the shell over the tubes and water, for steamgeneration, or steam for superheating is passed through the tubes. Inthis case the heat exchange is between fluids which will react violentlyif they come into contact for example by escape of steam or water intothe bulk sodium in the shell through a faulty tube/tube plate weld.Current designs of sodium/water heat exchangers rely on the excellenceof tube and tube/tube plate weld production and inspection to provide ahigh degree of integrity. However, the possibility of a major sodiumwater reaction has to be allowed for and it is therefore necessary todesign the heat exchanger shell to withstand the substantial internalpressures which would arise on the occurrence of such a reaction. Thusthe heat exchanger shallfand the tube plates have to be made ofconsiderable thickness.

Copending U.S. Pat. application Ser. No. 20,903, now U.S. Pat. No.3,680,627 relates to a tube-inshell" type of heat exchanger in which thehigh pressure water/steam is accommodated in the shell and the sodiumwithin the tubes, so that tube failure cannot propogate by overheatingand corrosion of further tubes adjacent to the failed tube. In this caseas the high pressure medium is contained within the shell, the shell andtube plates again have to be of considerable thickness to withstand thehigh internal pressure.

Also in tube in shell" type heat exchangers means have to be providedtoaccommodate for differential longitudinal thermal expansion of the tubesrelative to the shell both on rise to the steady thermal state and undertransient conditions. This can be achieved by making the tubes ofU-shaped configuration within the shell, with both tube plates locatedat the one end of the shell. In another arrangement the tubes are of .lor hockey stick configuration within a shell of similar shape, so thatthe tube plate at one end of the shell is in a plane at right angles tothe plane of location of the tube plate at the other end of the shell.Both these solutions add to the cost and complication of manufacture ofsuch heat exchangers.

SUMMARY OF THE INVENTION According to the present invention, in a tubein shell" heat exchanger, each tube plate is secured along its outeredge to the shell of the heat exchanger by an intermediate annularmember extending across a gap between the outer edge of the tube plateand the shell, the radial cross-section of the annular member being ofarched form.

Preferably the radial cross section of the annular member issemi-circular so that the annular member is in the form of half of atubular toroid. The annular member is preferably arranged with its innerand outer edges substantially in the plane in which the tube plate lies,the inner and outer edges of the annular member being joined with thetube plate and the shell by welding. The arched radial cross section ofthe annular member makes it of a high pressure containing capacity sothat the annular member can be made of relatively thin material. Thusthe annular member has a degree of flexibility in the direction normalto the plane of the tube plateso that the tube plate can movelongitudinally with respect to the heat exchanger shell, to accommodatefor relative longitudinal thermal expansion between the heat exchangertubes and the shell. In order to increase the flexibility of the annularmember whilst retaining the pressure retaining capacity, the annularmember can be made of laminated form.

Furthermore, in such sodium/water heat exchangers of the tube in shelltype wherein heated sodium is passed through the heat exchanger tubesand water is passed through the shell over the tubes for the generationof steam, it is advantageous to also provide thermal insulation on thefaces of the tube plates inside the shell, since the tube plates aresimultaneously in close thermal contact with sodium and water or steam.The thermal insulation is effective to minimise steady state thermalstresses in the tube plates as well as transient stresses due to suddenchanges in operating conditions. In particular the tube plate at thesteam outlet end of the heat exchanger shell, if uninsulated, would beexposed toparticularly severe conditions, since if the steam were wetliquid droplets would impact on the tube plate through which sodium ispassing at the high inlet temperature.

A known form of thermal insulation structure comprises a number ofbaffle plates arranged parallel to the tube plate and parallel to eachother. The baffle plates are drilled for penetration kby the tubes attheir ends adjacent the tube plate and are arranged to ensure thatstagnant fluid, ie steam or water, is trapped in spaces between thebaffle plates to provide the required thermal insulation.

This type of thermal insulation structure has a main disadvantage ofhigh cost of manufacture, since it is necessary to drill severalthousands of holes in the baffle plate for penetration of the baffleplates by the ends of the heat exchanger tubes. The economic penalty isparticularly high where a high degree of thermal insulation is requiredwhich is achieved by the provision of such a thermal insulationstructure consisting of a substantial number of baffle plates. A furtherpossible disadvantage stems from the fact that the spaces between thetube plates have only llimited access to the main body of the heatexchanger shell. Thus rapid evaporation of water in the spaces betweenthe baffle plates, on start up of the heat exchanger, or due to atransient change in the operating conditions, might lead to a rapidpressure build up in the spaces which cannot readily be relieved byventing from the spaces between the baffle plates to the main body ofthe shell. Thus there could be danger of local tube failure due toexcessive pressure build up.

According to a further feature of the present invention, the tube platesof a tube-inshell type heat exchanger as aforesaid have thermalinsulation comprising a series of plate members edge on to the tubeplate and arranged parallel one to another between successive `rows ofthe heat exchanger tubes. Where straight 3 runs exist between the rowsof tubes the plate members can be of plane form. In the case of a heatexchanger having closely pitched tubes where no straight runs existbetween the tubes the plate members may be of convoluted form so as tofit between the rows of tubes. This arrangement ensures that each heatexchanger tube at its point of connection'with the tube plate isenclosed in stagnant fluid either steam or water according to theconditions, which is trapped in the pockets defined between 'the'platemembers and the tubes. Thus a change of conditions leading to rapidevaporation of water trapped in the pockets cannot produce local excesspressure since each of the pockets is fully open to the main body of theshell. k

The said thermal insulation also has the advantage of cheapness since,for instance, it is not necessary to drill large numbers of holes in aseries of plates to produce the necessary baffles. The degree of thermalinsulation achieved is merely dependent on the depth of the platemembers. A high degree of thermal insulation can be achieved by simplymaking the plate members of sufficient depth. Also the thermalinsulation of the invention is easy to assembly with respect to the tubeplates it merely being necessary to interpose the series of platemembers edge on to the tube plate between parallel rows of the heatexchanger tubes. The plate members forming the insulation may besupported from their ends by a ring mounted on the face of the tubeplate encircling the heat exchanger tubes. Alternatively a supportingring for the plate members may be mounted around the inner wall of theheat exchanger shell just beneath the level of the tube plate.

DESCRIPTION OF THE DRAWINGS An embodiment of the invention will now bedescribed by way'of example with reference to the accompanying drawingsin which:

FIG. l is a longitudinal section of a heat exchanger incorporating thepresent invention,

FIG. 2 is an enlarged longitudinal section illustrating a modificationof the tube/tube plate assembly of the heat exchanger shown in FIG. l,

FIG. 3 is a section along the line III-III in FIG. 2, and

FIG. 4 corresponds to FIG. 3 and shows, on a larger scale, a detail ofan alternative arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The heat exchanger shown in theFIG. l of the drawings comprises a cylindrical shell l containing abundle of parallel heat exchanger tubes 2. The heat exchanger tubes 2extend longitudinally through the shell l between tube plates 3 locatedat each end of the shell l. The heat exchanger tubes 2 are spaced andtransversely located in the shell l, either by grids at spaced intervalsalong the length of the tubes l, or, alternatively, the tubes 2 may bespaced by being wire wrapped or by integral tins on the tubes the tubesbeing held together in the bundle by an outer wrapper arrangement suchas is disclosed in said copending application Ser. No. 20,903.

The shell l has an inlet branch 4 at its lower end and an outlet branch5 at its upper end. The tubes 2 extend through holes 6 in the tube plate3 at the upper end of the shell l and connect at their upper ends withan inlet header 7. Similarly the tubes 2 extend through holes 6 in thetube plate 3 at the lower end of the shell l and connect at their lowerends with an outlet header 8. The tubes 2 are brazed in passage throughthe holes 6 in the tube plates 3 and are also brazed at their ends inconnection with the inlet and outlet headers 7 and 8.

Each of the tube plates 3 is connected with the shell l in a similarmanner. Referring to the tube plate 3 at the upper end of the shell l,the tube plate 3 is of smaller outside diameter than the internaldiameter of the upper end of the shell l so that an annular gap 9 existsbetween the outer'edge of the tube plate l and the edge of the shell l.Thegap 9 is bridged by an annular member l() which is of semi-circularradial cross section. The member 10 may be described as being in theform of half a tubular toroid and is made up of several nestinglaminations ll. The member l0 is joined at its inner edge 12 with theouter edge of the tube plate 3 by a weld 13. The member 10 is joined atits outer edge 14 with the edge of the shell 1 by a weld l5.

In use of the heat exchanger, for example as a once through boiler,water is passed into the shell l through the lower inlet branch 4 andsteam is generated in the shell l by heat exchange with, for example,heated sodium which is passed through the heat exchanger tubes 2. Theheated sodium is passed into the tubes 2 through the upper inlet header7 and after passing downwards through the heat' exchanger tubes 2 passesout through the lower outlet header 8. Steam generated for example atapressure of 2,500 psi in theshell 1 passes out of the shell l throughthe upper outlet branch 5.

There will be a high axial pressure force acting on the tube plates 3but the heat exchanger tubes will carry the main part of this axialpressure force by being under longitudinal tension. Therefore the tubeplates 3 can be of relatively small thickness, for example 3 inches ascompared with a thickness of l2 inches which would be required for tubeplates which carry the whole of the internal pressure back to the shelll.

The shape of the annular members 10 makes it possible to contain thehigh internal pressure in the shell l with a relatively smallthicknessof metal in the annular members l0. Due to geometrical factors andbecause the annular members 10 are of relatively thin laminations ll theannular member l0 have flexibility in the direction of the longitudinalaxis of the shell l ie in the direction normal to the plane of the tubeplates 3. This allows the tube plates 3 to move longitudinally withrespect to the heat exchanger shell l, by flexing of the annular members10, to accommodate for longitudinal thermal expansion of the heatexchanger tubes 2 relative to the shell l. Longitudinal thermalexpansion of the heat exchanger tubes 2 relative to the shell l occursdue to the temperature differential which arises between the tubes 2 andthe shell l on bringing the heat exchanger to its state of operatingtemperature.

The heat exchanger of the invention has the advantage of ease ofassembly as the tubes 2 can be assembled with the tube plates 2 outsidethe heat exchanger shell l and the assembly of the tubes 2 and tubeplates 3 can then be inserted into the shell l and the tube plates 3connected with the ends ofthe shell l by welding the annular members l0bridging the gap 9 between the tube plates 3 and the ends of the shelll. The laminations ll of the annular members l0 may be weldedindividually one by one into position or alternatively the laminationsl1 may be welded to separate rings, the

- and the shell 1. This latter procedure eases the inspection and heattreatment of the lamination welds.

The modified tube/tube plate assembly shown in FIGS. 2 and 3 of thedrawings comprises a tube plate 21 with which there is connected aseries of heat exchanger tubes 22. The heat exchanger tubes 22 arearranged in a bundle parallel to one another and are welded at theirends in connection with holes 23 in the tube plate 21. A heat insulationstructure for the under face of the tube plate 2l comprises a series ofparallel plates 24 arranged edge on to the face of the tube plate 2l.The plates 24 are interposed between parallel rows of the heat exchangertubes 22. A supporting ring 2S for the plates 24 is welded to the faceof the tube plate 21 encircling the bundle of heat exchanger tubes 22.The ends of the plates 24 rest on an internal flange 26 at the bottom ofthe ring 25. The bundle of heat exchanger tubes 22 is fitted inside theshell l (FIG. l) to which the tube plates at either end of the bundle oftubes 22 are secured via the annular members l0 (FIG. l). y

Where the heat exchanger is of sodium/water type, heated sodium ispassed through the heat exchanger tubes 22 and water for the generationof steam is passed through the shell l over the tubes 22.

The thermal insulation structure of the invention provides thermalinsulation for the tube plates 21 by the trapping of stagnant steam orwater in the pockets defined at the face of the tube plates between theplates 24 and the ends of the heat exchanger tubes 22.

In the arrangement of FIG. 3, straight paths exist between the rows ofheat exchanger tubes 22 so that the plates 24 can be of plane form. Inthe alternative arrangement of FIG. 4, the tubes 22 are of closer pitchso that there are no straight paths between the rows of tubes. In thiscase the plates 24' are made of convoluted or corrugated form to fitbetween the tubes 22.

I claim:

l. In a tube-in-shell heat exchanger in which a bundle of parallel heatexchanger tubes extend between tube plates at either end of the bundle,said tubes being connected with holes in the tube plates, and a shellwithin 6 which said bundle of tubes is disposed with means for securingsaid tube plates to said shell, the improvement wherein said means forsecuring each tube plate to said shell comprises an annular memberintermediate each said tube plate and said shell, said member beingsecured to the outer edge of the respective tube plate and .to saidshell to extend across a gap therebetween, and

the radial cross section of said annular member being of arched form.

2. A heat exchanger according to claim l, characterised by the radialcross section of said member being semi-circular.

3. A heat exchanger according to claim 2, characterised inl that saidannular member is arranged so that its inner and outer edges aresubstantially in the plane in which the respective tube'plate lies andare joined with said tube plate and said shell by welding.

4. A heat exchanger according to claim l, characterised by said annularmember being made of laminated form.

5. A heat exchanger according to claim l, characterised by said tubeplates each having thermal insulation comprising a series of individualand mutually isolated plate members edge on tothe respective tube plateand arranged parallel to one another between successive rows of the heatexchanger tubes.

6. A heat exchanger according to claim 5., characterised by said platemembers being plane for extending in straight runs between said tubes.

7. A heat exchanger according to claim 5, characterised by said platemembers being of convoluted form for extending between said tubes wherethese are closely pitched.

8. A heat exchanger according to claim 5, characterised by said platemembers being supported from their ends by a ring mounted on the face ofthe respective tube plate and encircling said heat exchanger tubes.

9. A heat exchanger according to claim l wherein the inner periphery ofsaid annular arched member is secured to the outer edge 0f therespective tube plate, and the outer periphery of said member is securedto said shell.

1. In a tube-in-shell heat exchanger in which a bundle of parallel heatexchanger tubes extend between tube plates at either end of the bundle,said tubes being connected with holes in the tube plates, and a shellwithin which said bundle of tubes is disposed with means for securingsaid tube plates to said shell, the improvement wherein said means forsecuring each tube plate to said shell comprises an annular memberintermediate each said tube plate and said shell, said member beingsecured to the outer edge of the respective tube plate and to said shellto extend across a gap therebetween, and the radial cross section ofsaid annular member being of arched form.
 2. A heat exchanger accordingto claim 1, characterised by the radial cross section of said memberbeing semi-circular.
 3. A heat exchanger according to claim 2,characterised in that said annular member is arranged so that its innerand outer edges are substantially in the plane in which the respectivetube plate lies and are joined with said tube plate and said shell bywelding.
 4. A heat exchanger according to claim 1, characterised by saidannular member being made of laminated form.
 5. A heat exchangeraccording to claim 1, characterised by said tube plates each havingthermal insulation comprising a series of individual and mutuallyisolated plate members edge on to the respective tube plate and arrangedparallel to one another between successive rows of the heat exchangertubes.
 6. A heat exchanger according to claim 5, characterised by saidplate members being plane for extending in straight runs between saidtubes.
 7. A heat exchanger according to claim 5, characterised by saidplate members being of convoluted form for extending between said tubeswhere these are closely pitched.
 8. A heat exchanger according to claim5, characterised by said plate members being supported from their endsby a ring mounted on the face of the respective tube plate andencircling said heat exchanger tubes.
 9. A heat exchanger according toclaim 1 wherein the inner periphery of said annular arched member issecured to the outer edge of the respective tube plate, and the outerperiphery of said member is secured to said shell.